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    <title>ss2des</title>
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    <center>Scilab Function</center>
    <div align="right">Last update : April 1993</div>
    <p>
      <b>ss2des</b> -  (polynomial) state-space to descriptor form</p>
    <h3>
      <font color="blue">Calling Sequence</font>
    </h3>
    <dl>
      <dd>
        <tt>S=ss2des(Sl)  </tt>
      </dd>
      <dd>
        <tt>S=ss2des(Sl,flag)  </tt>
      </dd>
    </dl>
    <h3>
      <font color="blue">Parameters</font>
    </h3>
    <ul>
      <li>
        <tt>
          <b>Sl</b>
        </tt>: <tt>
          <b>syslin</b>
        </tt> list: proper or improper linear system.</li>
      <li>
        <tt>
          <b>flag</b>
        </tt>: character string <tt>
          <b>"withD"</b>
        </tt>
      </li>
      <li>
        <tt>
          <b>S</b>
        </tt>: list</li>
    </ul>
    <h3>
      <font color="blue">Description</font>
    </h3>
    <p>
    Given the linear system in state-space representation 
    <tt>
        <b>Sl</b>
      </tt> (<tt>
        <b>syslin</b>
      </tt> list), with a <tt>
        <b>D</b>
      </tt> matrix which is either
    polynomial or constant, but not zero <tt>
        <b>ss2des</b>
      </tt>
    returns a descriptor system as <tt>
        <b>list('des',A,B,C,0,E)</b>
      </tt>
    such that:</p>
    <pre>

Sl=C*(s*E-A)^(-1)*B
   
    </pre>
    <p>
    If the flag <tt>
        <b>"withD"</b>
      </tt> is given, <tt>
        <b> S=list('des',A,B,C,D,E) </b>
      </tt>
    with a <tt>
        <b>D</b>
      </tt> matrix of maximal rank.</p>
    <h3>
      <font color="blue">Examples</font>
    </h3>
    <pre>

s=poly(0,'s');
G=[1/(s+1),s;1+s^2,3*s^3];Sl=tf2ss(G);
S=ss2des(Sl)
S1=ss2des(Sl,"withD")
Des=des2ss(S);Des(5)=clean(Des(5))
Des1=des2ss(S1)
 
  </pre>
    <h3>
      <font color="blue">See Also</font>
    </h3>
    <p>
      <a href="../polynomials/pol2des.htm">
        <tt>
          <b>pol2des</b>
        </tt>
      </a>,&nbsp;&nbsp;<a href="../robust/tf2des.htm">
        <tt>
          <b>tf2des</b>
        </tt>
      </a>,&nbsp;&nbsp;<a href="../robust/des2ss.htm">
        <tt>
          <b>des2ss</b>
        </tt>
      </a>,&nbsp;&nbsp;</p>
    <h3>
      <font color="blue">Author</font>
    </h3>
    <p>F. D.; ;   </p>
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